This invention relates to the field of threaded bolts, screws, and nuts. More particularly, the invention pertains to a bolt having a tapered end with partial threads that engages an oval shaped nut having internal elongated adjacent sides, thereby allowing for uninhibited insertions of the bolt into the nut to ensure threaded engagement that will preclude cross threading.
Generally, there is little or no difficulty in starting a threaded bolt into a nut when the two mating parts have their longitudinal axes aligned. However, when the bolt enters the threaded part of the nut which is misaligned angularly with respect to the axis of the threaded bolt, the threads may initially engage incorrectly. Thereafter, as the bolt is driven towards full engagement, the threads of the bolt and/or nut fail by shearing and often the bolt is severed. This condition is called cross threading.
If the axis of the bolt is excessively misaligned angularly with respect to the longitudinal axis of the nut, The person engaging the bolt may readily perceive the misalignment because the threads failed to engage. Accordingly, corrective action is taken to align the bolt with the nut. However, when the misalignment is slight, the person driving the bolt forward may not be aware that the first bolt threads are in opposition to the first nut threads engagement in such a way that cross threading occurs. In cases such as these, the bolt is removed from the nut, and the nut threads are retapped or the nut is replaced, resulting in lost production, lost time incurred when making the necessary replacement, the cost of bolts and/or nuts, and in incidental repairs to related equipment.
Furthermore, cross threading occurs more frequently where power tools are used to drive a threaded bolt as is the case in production line assembly plants. To avoid this difficulty, a plant worker or craftsman may manually start the bolt threads into the nut to assure proper engagement of the first few bolt threads with those of the nut. Then, a power tool is attached to a socket that engages the bolt head or nut and the threading process is then completed. When conventional bolts are used and angular misalignment of the bolt is excessive, potential for cross threading is great unless the plant worker corrects the alignment problem before the power tool is applied to drive the bolt or nut to a fully engaged position. Cross threading can make it very difficult to disengage the bolt and nut resulting in considerable expense in the operation of large scale production line assemblies due to delays to replace damaged bolts and nuts, and even more critical where work is being performed upon equipment in the field or under adverse conditions.
Additionally, if cross threading is not corrected, the threads on both the bolt and the nut may seize together causing them to jam or produce a cold flow reaction. Once the bolt and nut combination have seized, it will not tighten further creating an insecure attachment which if undetected may result in unpredictable ways or forms of hazards with more or less disastrous consequences to life, limb and property.
The subject invention herein solves all of these problems in a new and unique manner which has not been part of the art previously. Some related patents are described below:
U.S. Pat. No. 4,789,288 issued to F. C. Peterson on Dec. 6, 1988
This patent discloses an anti-cross threading screw. The anti-cross threading screw comprises a head having a load bearing area, and a threaded cylindrical shank extending perpendicularly from the load bearing area. The tip of the shank is tapered in the offset. The screw prevents cross-threading because the non-threaded side of the screw slides over the internal threading of a nut when the screw tip is inserted into a nut, causing the partial threads to seat against the nut internal threading.
U.S. Pat. No. 5,073,073 issued to H. Kazino et al on Dec. 17, 1991
The patent is directed to a self-aligning bolt and a self-aligning nut. The bolt comprises a threaded shank extending from a head, and a pilot tip extending forwardly of the threaded shank. The pilot tip includes an intermediate portion for smoothly connecting to the threaded shank.
U.S. Pat. No. 4,973,209 issued to C. Essom et al on Nov. 27, 1990
This patent is directed to a screw for contaminated pretapped holes. The screw includes a full width non-tapered tubular shank section, a tapered tubular trunk and entry section extending from shank section, and a cylindrical tip.
U.S. Pat. No. 4,952,110 issued to Avooustis et al on Aug. 28, 1990
This patent discloses an anti-cross thread bolt. The bolt includes a head, a threaded shank projecting from the head, and a tip at the end of the shank opposing the head. The tip includes a non-threaded relatively smooth portion and a partially threaded portion. The smooth portion of the tip has an arcuate peripheral surface.
U.S. Pat. No. 4,981,406 issued to R. G. Weiss et al on Jan. 1, 1991
The patent is directed to a threaded fastener. The threaded fastener comprises a threaded shank extending from a head. The lower end of the shank has a tapered transition surface.